Notoriety

Born in Algeria, Belmokhtar was a former senior figure in al-Qaeda in the Islamic Maghreb (AQIM), but left to form his own militia.

He gained notoriety with the attack on the In Amenas gas plant in Algeria in 2013, when about 800 people were taken hostage and 40 killed, most of them foreigners, including six Britons and three Americans.

The US has filed terror charges against him and officials said they believed he remained a threat to Western interests.

"Belmokhtar has a long history of leading terrorist activities as a member of AQIM, is the operational leader of the al-Qaeda-associated al-Murabitoun organisation in north-west Africa, and maintains his personal allegiance to al-Qaeda," said Pentagon spokesman Col Steve Warren.

Analysis: Jonathan Marcus, BBC Diplomatic Correspondent

Dead, or maybe still alive, either way the fact that the US is still hunting Mokhtar Belmokhtar illustrates the breadth and tenacity of the US counter-terrorism effort.

While the focus is now very much on combating Islamic State in Iraq and Syria, the US struggle against al-Qaeda franchises continues both in the Middle East (Libya in this case) and to a growing extent in sub-Saharan Africa too.

Belmokhtar masterminded the attack on the Amenas gas plant in Algeria in 2013 in which 40 people were killed, including three Americans.

He was targeted not in a drone strike but an attack launched by two F-15 aircraft.

Libya looks set to be an area of renewed concern for the Americans, the instability prompted by the removal of Muammar Gaddafi in 2011 providing a rich vein of ungoverned space in which various Islamist militants, including Islamic State are establishing a significant presence.